Conventionally, as dedicated eyeglasses for a color-blind person to distinguish between red and green, there are eyeglasses using, for example, a red filter (or green filter). However, using such dedicated eyeglasses are not preferred by a color-blind person because it enables others to recognize that he/she is color-blind. Further, since a color-blind person generally uses the dedicated eyeglasses only when there is a need to distinguish between red and green, taking on and off the eyeglasses from time to time is very cumbersome.
PTL 1 discloses electronic sunglasses capable of controlling various colors displayed by using liquid crystal materials for each of red, green, and blue. The electronic sunglasses are, however, for use as sunglasses that display color according to user's taste, such as individual's preference, location, and fashion, and no consideration is given to the application as dedicated eyeglasses for a color-blind person. Further, the control structure of the electronic sunglasses uses a cholesteric liquid crystal material to reflect light having a certain wavelength, and the complexity of the structure and necessity of a large number of components make the electronic sunglasses impractical.
PTL 2 relates to the field of liquid crystal display panels instead of eyeglasses, but discloses a color liquid crystal display element which uses a nematic liquid crystal material having a specific refractive index. As an example of prior art, PTL 2 describes in paragraph [0002] that a color liquid crystal display element composed of a liquid crystal cell including color filters and a pair of polarizing films sandwiching the liquid crystal cell performs color display by changing optical transmittance on a color filter basis. PTL2 further describes in paragraph [0004] that a conventional color liquid crystal display panel using color filters produces colored light by causing the color filters to absorb light having a specific wavelength and, therefore, the amount of transmitted light decreases and display becomes dark. In other words, PTL 2 investigates only the performances of the display panel, and no consideration is given to the use of the display panel for eyeglasses or other applications.